The present invention relates to the production of 1,1,1-tris(4'-hydroxyphenyl)ethane (THPE) or more particularly to a method of purifying 1,1,1-tris(4'-hydroxyphenyl)ethane. It is known in the art that 1,1,1-tris(4'-hydroxyphenyl)ethane may be produced by reacting 4-hydroxyacetophenone with phenol. Typically this is performed with phenol also used as the solvent for the mixture. The reaction proceeds under acidic catalytic conditions such as a co-catalyst system of hydrochloric acid and beta-mercaptopropionic acid. A problem with this reaction is that the yield is relatively low, i.e. only about 70-80% and the product contains substantial amounts of impurities. These include iso-THPE which is a mixture of ortho- and para-tris(hydroxyphenyl)ethane isomers, 1,1-bis(hydroxyphenyl)ethene isomers, phenol, 4-hydroxyacetophenone, chloride, as well as unidentified color bodies and light and heavy ends. Although pure THPE is white, the reaction product is a reddish-brown mixture of pure and impure product. THPE is used as a hardener for epoxies and as a crosslinker for polycarbonates. As such, its color must be white. The present invention provides a purification process which uses only a single recrystallization from methanol/water. It has been found that white and very pure THPE will be obtained if the crude reaction mixture is washed with a THPE saturated wash/methanol liquid prior to the single recrystallization or more preferably with the wash filtrate liquid of a preceding recrystallization although this is colored and rich in the above mentioned impurities. It has been found that by use of such a wash yields of pure and white THPE are good, and solvents have a more productive use. On the other hand only a single recrystallization is necessary if the crude THPE is initially washed with the filtrate from a preceding recrystallization.
The results of the filtrate wash and the following single recrystallization are dependent on the phenol content prior to the wash. By washing the highly colored crude THPE with filtrate from a prior THPE recrystallization, phenol can be removed from the crude cake almost quantitatively. Although the filtrate is saturated with THPE, the recovery of THPE is not quantitative due to the dissolving effect of phenol during the initial wash. A higher recovery is observed for a crude admixture with a lower phenol content. In general lower phenol content raises THPE recovery, however, if phenol content is too low, impurities are not removed satisfactorily. A crude admixture having a phenol content of about 5% maximized recovery of exceedingly pure THPE.
As a result of the process, most of the color bodies are removed in the wash stage where the color of the crude THPE changes from a dark rusty color to a light tan. The balance is removed in the recrystallization. Best results are obtained when the recrystallization filtrate has a water content which has been adjusted to between 60 and 75%. The use of a higher amount of water gives higher THPE recoveries, but the material fails to meet the white color requirement in the following single recrystallization.
For the crude THPE washed with recycled recrystallization filtrate, only a single recrystallization from methanol/water is necessary to meet the white color and high purity requirements. This recrystallization is basically a precipitation of THPE from the methanol/water solution. The simplicity of this purification procedure was very unexpected with respect to the complexity of the crude mixture and the close similarity of some components of the crude mixture. Thus, this procedure is substantially low in labor and capital costs. In another embodiment of the invention, if a partial phenol removal from the crude reaction product is performed prior to the wash, the process has some increased costs compared to the simple wash/single recrystallization process, but there is a substantially higher refining recovery. In either case, waste management is simplified because phenol and chloride containing waste water streams from hot water washes are avoided, and the other waste streams can be substantially minimized.